This invention relates to the preplating and electroplating of plastic sheaths covering a conductive core to form coaxial cable.
U.S. Pat. No. 3,681,511 discloses a process comprising subjecting a substrate to a member of the group of elemental phosphorus and low oxidation state phosphorus compounds, and thereafter to a metal salt or complex thereof in order to provide a coating on the substrate for use in the production of electrostatic and magnetostatic shielded wires and antistatic textiles. Although the process can be used in a laboratory, it has been found that in large scale continuous operations, electroplating the plastic sheaths using conventional apparatus may result in the cracking of the electroplated layer.
U.S. Pat. No. 3,579,430 discloses an apparatus for electroplating in which copper wire is tinned prior to being covered by insulating material. This apparatus basically comprises a double trough system in which a smaller plating trough is enclosed in a larger overflow trough. The untrimmed wire is advanced horizontally through the trough and has contact only with the solution by virtue of the external support of pulley on either end of the outside trough which maintain the desired tension in the wire. A disadvantage of this apparatus is that the anodes are not symmetrical with respect to the geometry of the wire to be electroplated. Since electroplating on plastics, as opposed to electroplating wire, may require more critical adjustment of the geometric configurations of the apparatus, this could be a critical disadvantage.
A possible solution to this problem is to use a T-tube. Although the use of T-tubes generally in plating operations is old, such use has been confined to electroless plating in which no anodes are needed. While it may be apparent that the particular geometry of the T-tube is compatible with the geometry of the plastic sheathed wire, it has not been apparent what combination of tube and anode configuration would allow the production of coaxial cable in commercial quantities.